[SIGCIS-Members] Question about the Tiltman break in Lorenz cypher (1941)

Mon May 24 07:27:49 PDT 2021

Emmanuel -

I don't know if the cyphertexts have been wrongly transcribed or not, but
for sure Friedrich Bauer made a slip when he added them together, as I
described in my earlier post (did you see that?).

If the originals exists, they might be in the Bletchley Park archives.
Their website https://bletchleypark.org.uk/ has some information about
their collections and archives, and contact details.

Best
Mark

On Mon, 24 May 2021 at 14:41, E. Lazard <Emmanuel.Lazard at dauphine.psl.eu>
wrote:

> Many thanks for your answers.
>
> Le 24 mai 2021 à 04:38, thomas.haigh at gmail.com a écrit :
>
> I wonder if the problem is in part that Copeland got the teleprinter
> character set wrong. Some years ago I was working from the version given in
> his appendix when trying to understand the quirks in the interaction of
> German and the teleprinter code that explained why the deltas between the
> bit patterns for successive characters were both much more likely to be 0
> than 1. That is what underpinned Tutte's method, used by Colossus, which
> exploited the fact that the deltas between successive characters were not
> fully scrambled by the Lorenz equipment. So there was a clear statistical
> signature that marked the correct positions for the first two "Chi wheels."
> (That analysis underpinned my attempt to give an accurate but
> non-mathematical account of the process in
> https://cacm.acm.org/magazines/2017/1/211102-colossal-genius/fulltext).
>
> I was having some difficulty in squaring tables in archival reports giving
> the most common two letter sequences in the encoded messages with the bit
> patterns for the deltas between them. Then I realized, or my collaborator
> Mark Priestley pointed out, that the discrepancies were caused by errors in
> the teleprinter alphabet Copeland included as appendix 2 on pages 248-9.
> Five years on I can’t remember if there was just one error or several. But
> I do remember that the frequency of EI in the plaintext was very high so I
> just  rechecked that his entries for those letters. I see that the code
> Copeland gives for I (oxxox) does not match the one given at
> https://en.wikipedia.org/wiki/Baudot_code. The other clue is that
> Copeland has the same bit pattern in successive lines, identified first as
> coding P and then as coding I. They can't both be right.
>
> Looking at the
> https://billtuttememorial.org.uk/codebreaking/teleprinter-code/ page that
> Emmanuel mentions, I notice a similarly blatant error: the page identifies
> both M and N as being coded by (ooxxx). Which doesn't match Copeland or
> Wikipedia. So it appears that both the Tutte fan site and the Copeland book
> present incorrect teleprinter alphabets.
>
>
> I’ve checked in my copy of the Copeland book and indeed, the I code isn’t
> correct:  it’s given as •xx•x (same as P) but it should be •xx••.
> It’s the only mistake in the book (concerning the Baudot code) and it
> doesn’t solve my issue where I isn’t involved…
>
>
>  Hence Emanuel shouldn't discount the possibility that the cyphertexts
> are correct but the teleprinter code to bit conversions are wrongly given
> in both the sources he is relying on. Having said that, given the rather
> low standards of proofreading we're seeing here it wouldn't shock me if the
> cypher text sequences were also given wrongly in Copeland and copied from
> one website to another with errors included. I don't have time to check
> back to primary sources, but if I was doing serious work on the
> technicalities of this, I'd either dig into the archival sources or at
> least work as much as possible from Reeds, James A., Whitfield Diffie, and
> J V Field. Breaking Teleprinter Ciphers at Bletchley Park. An Edition of
> General Report on Tunny With Emphasis on Statistical Methods (1945).
> Piscataway, NJ: IEEE Press/Wiley, 2015  (
> https://www.amazon.com/Breaking-Teleprinter-Ciphers-Bletchley-Park/dp/0470465891).
> This is a heavily annotated and supplemented reprint of a formerly secret
> report written as the operation was being wound down at the end of the war.
> Chapter 41-44 give a thorough description of the original methods used
> prior to mechanization. (Though not, as far as I can see on a quick look,
> the full text of the messages in question).
>
> Regarding one of Brian's comments, IIRC "addition" was simply what the BP
> staff called the operation we're more used to thinking of as XOR. So that
> might not be a source of error. They also spoke of dots and crosses rather
> than 1 and 0. It’s just more natural for us today to XOR 1s and 0s than to
> add dots and crosses. Brian is right about the shift codes, which helped to
> create some of the regularities in the deltas exploited by the
> codebreakers. IIRC, however, the shift codes get encrypted just like the
> other characters, rather than being stripped out by the Lorenz equipment
> prior to encryption as he suggests.
>
>
> Brian’s code is just a NOT-XOR, which is just symmetrical. For the
> operations, exchanging 1’s and 0’s is completely irrelevant, so using XOR
> or its opposite doesn’t change anything.
>
> So I’m more and more convinced that the ciphertexts have been wrongly
> given and copied from one website to the other… I’ve of course read the
> "general report on Tunny" but unfortunately, the ciphertexts are not given
> in it. So I guess I would have to dig through the archives… Any idea whom I
> may contact?
>
> Regards
> Emmanuel
>
>
>
>
>
>
>
>
> -----Original Message-----
> From: Members <members-bounces at lists.sigcis.org> On Behalf Of Brian E
> Carpenter
> Sent: Sunday, May 23, 2021 6:52 PM
> To: E. Lazard <Emmanuel.Lazard at dauphine.psl.eu>; members at sigcis.org
> Subject: Re: [SIGCIS-Members] Question about the Tiltman break in Lorenz
> cypher (1941)
>
> Emmanuel,
>
> On 24-May-21 09:47, E. Lazard wrote:
> > Dear all,
> >
> > I’m looking for some original information on the famous "Tiltman break"
> which led to the cryptanalysis of the Lorenz cipher en 1941.
> > (https://en.wikipedia.org/wiki/Cryptanalysis_of_the_Lorenz_cipher
> > <https://en.wikipedia.org/wiki/Cryptanalysis_of_the_Lorenz_cipher>)
> > (http://www.eprg.org/computerphile/lorenz-combined.pdf
> > <http://www.eprg.org/computerphile/lorenz-combined.pdf>)
> >
> > The story is: the British intercepted two messages sent with the same
> key (HQIBPEXEZMUG) also called a "depth".
> > When adding the two cipher texts with the exclusive-or function, the key
> cancels out and what is left is the exclusive-or of the two plain texts.
> > From there, brigadier John Tiltman found the two messages by trying
> various likely pieces of plaintext and found that the first message started
> with the word SPRUCHNUMMER (message number) and that the second message
> also used the same word but shortened out as SPRUCHNR.
> >
> > EVERY SINGLE WEBSITE and the Copeland book "Colossus" list the two
> intercepted cypher texts as:
> >
> > C1 = JSH5N ZYMFS 01151 VKU1Y U4NCE JEGPB
> > C2 = JSH5N ZYZY5 GLFRG XO5SQ 5DA1J JHD5O
> >
> > and their exclusive-or as:
> >
> > D  = ///// //FOU GF14M AQSG5 SEKZR /YWHE
>
> Indeed,  S and 5 combine to give V according to
> https://billtuttememorial.org.uk/codebreaking/teleprinter-code/
> > My problem is that IT DOES NOT ADD UP!
> > The U in 10th position is not the correct result, it should be a V.
> > (S is 10100, 5 is 11011, so their exclusive-or is 01111 which is V)
>
> However, there are two problems with your comment:
>
> 1) The code for 5 is actually 11110, the same as the code for T, but in
> figure shift. I assume that the Lorentz system removed the figure shift and
> letter shift codes before starting the crypto work.
> 11011 is indeed the figure shift code, so the actual bit stream would have
> contained 11011 11110 11111.
>
> 2) The appropriate operation is not XOR. It's what Bletchley Park called
> "addition", as described at the above web site. While that doesn't explain
> this U/V error, which I suppose started as a transcription error, it
> probably explains the other errors you mention.
>
> Regards
>    Brian Carpenter
>
> > And I found other issues with all examples using the cypher text, the
> messages, the key… I always have several letters which are wrong.
> >
> > So I’m wondering if I’ve misunderstood something or have the cypher
> texts been incorrectly written down once and everybody just copied them
> without checking?
> >
> > Anybody has genuine information or can point me to some source?
> >
> > Regards
> > Emmanuel Lazard
> >
> >
> >
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